Anyways, I was thinking about the processing time. It makes sense to me. It helps to reduce fraud, even though fraud still exists. I used to get my debit card numbers stolen all the time, and I think it had to do with this shady gas station, I used to go to.
Let us say, someone some how got your debit card information, starting charging things. Your bank sends you a notice, about transactions in a different part of a country, than where you live. You call them and tell them, that it's fraud. The bank stops the transaction and your account is safe, while also protecting more loss to the bank, and other retailers.
If transactions were instant, than a fraudster could charge a bunch of things, and the transaction was already instantly processed, with not much the bank could do, to mitigate loss. I think it's for security reasons, that transactions take a couple days to process by card, to prevent fraud. That's my take. It's not really a conspiracy.
Now, if digital transaction become more secure, like biometric finger printing, or some sort eye recognition, than yeah, maybe instant payments could be made. There is to much fraud in the world for instant processing, for banks to let this happen.